Zhonghua Shi

Three-Way Catalyst Meeting Euro III Emission Standards for Motorcycles

Abstract The Pt/Pd/Rh three-way catalyst was prepared using a high-performance Ce 0.55 Zr 0.35 Y 0.05 La 0.05 O 2 solid solution and high surface area La-stabilized alumina (La/Al 2 O 3 ). The activity and durability of the catalysts under simulated conditions and actual vehicle test conditions were studied. The results revealed that Ce 0.55 Zr 0.35 Y 0.05 La 0.05 O 2 solid solution maintains superior textual and oxygen storage properties, and La/Al 2 O 3 has superior textual properties. The catalyst had high low-temperature activity, wide air-to-fuel ratio windows, and good thermal stability. The results from the emission test of a motorcycle showed that the catalyst can meet Euro III emission requirements.

The Effect of La2O3 on Pd Close-Coupled Catalysts

Palladium close-coupled catalysts were prepared by impregnation method with different amounts of La2O3 as a promoter. Low temperature N2 adsorption-desorption, X-ray diffraction, H2-temperature programmed reduction (H2-TPR), CO-chemisorption, and X-ray photoelectron spectroscopy (XPS) were used to characterize the effect of La2O3 on the physicochemical properties of the prepared catalysts. Their catalytic activities toward C3H8 conversion were evaluated using a gas mixture that simulates the emissions from a gasoline engine. The results of catalytic activity indicate that the presence of La2O3 significantly improves catalytic performance and enhances the thermal resistance of the catalysts. H2-TPR results suggest that the addition of La2O3 increases the reductive ability of the catalysts and shifts the reduction temperature to a lower value. The XPS and CO-chemisorption results indicate that doping by La2O3 also improves the dispersion of the Pd species and decreases the mean particle size of palladium. The optimal loading amount of La2O3 is 10%.

Effect of surface tension on the properties of a doped CeO2–ZrO2 composite and its application in a Pd-only three-way catalyst

La and Pr modified ceria–zirconia solid solution materials CeO2–ZrO2–La2O3–Pr6O11 (CZLP) were synthesized through a co-precipitation method, in which the influence of surface tension during the drying process on the textural/structural properties, reduction behavior and oxygen storage capacity of the materials was investigated. The difference in catalytic performance of the supported Pd-only thee-way catalysts was further studied. The results revealed that CZLP3 obtained through a supercritical ethanol drying method which eliminated the surface tension in the drying process exhibited a texture with a larger pore size and wider pore size distribution. Such texture is crucial to improve the thermal stability and anti-aging ability of materials. After calcining at 1000 °C, the specific surface area, cumulative pore volume and average pore radius of CZLP3-a were 52 m2 g−1, 0.52 cm3 g−1 and 20.3 nm, respectively. The XRD and Raman results revealed that a more homogeneous solid solution of Ce, Zr, La and Pr was formed, and the aging-treatment-induced segregation of phases was inhibited for CZLP3. Besides, the slightest grain growth after the aging treatment shown in TEM images indicated the superior anti-aging ability of CZLP3. The Raman and XPS analysis demonstrated the highest concentration of oxygen vacancies and surface Ce3+ species for CZLP3 both before and after the aging treatment, which contributed to the enhancement of its reduction properties and oxygen storage capacity. Consequently, Pd/CZLP3 exhibited outstanding three-way catalytic activity compared with the others both before and after the thermal aging treatment, indicating its tremendous potential possibilities.

Effect of high temperature pretreatment on the thermal resistance properties of Pd/CeO2/Al2O3 close-coupled catalysts

Abstract Fresh Pd/CeO2/Al2O3 close coupled catalyst was prepared by the stepwise impregnation method and calcined at 550 °C for 3 h, which was then pretreated at 700, 800, and 900 °C for 3 h, respectively. Finally, these pretreated catalysts were aged at 1000 °C for 3 h to study their anti-aging properties. The catalytic activities of the catalysts were investigated detailedly, and the results showed that the catalyst pretreated at 800 °C before aging treatment possessed the best anti-aging performance for C3H8 oxidation. XRD and XPS results indicated that well-crystallized CeO2 particles were formed during calcinations at 800 °C, which made CeO2 an effective promoter. HRTEM revealed that Pd particles found on the edge of CeO2 over the aged catalyst pretreated at 800 °C were relatively smaller than those over the catalysts without pretreatment. H2-TPR and XPS results also implied that the interaction between well-crystallized CeO2 and Pd suppressed the deactivation of PdO sites and further enhanced the catalytic performance.

Designed synthesis of Zr-based ceria–zirconia–neodymia composite with high thermal stability and its enhanced catalytic performance for Rh-only three-way catalyst

Developing advanced oxygen storage materials that deliver high thermal stability is crucial to meeting increasingly stringent environmental regulations for three-way catalysts (TWCs). The surfactant, trialkylamine (N235, N (CnH2n+1), n = 8–10), was used to prepare the zirconium (Zr)-based ceria–zirconia–neodymia composites with loose morphology for the first time, and the effect of N235 on the properties of the ceria–zirconia–neodymia solid solution composites was investigated systematically. After thermal treatment at 1000 °C for 5 h in air, the obtained material (CZ/N235-1000) presented a high surface area of 31 m2 g−1 and had superior redox properties. As a support material in rhodium (Rh)-only TWCs, the prepared Rh/CZ/N235-f and Rh/CZ/N235-a demonstrated excellent catalytic performances. Particularly, after aging at 1000 °C for 5 h in air, the light off temperature (T50%) of nitrogen oxide and carbon monoxide for Rh/CZ/N235-a were 229 °C and 235 °C, respectively, and were much lower than those (278 °C and 280 °C) of Rh/CZ-a in which the support material was synthesized without N235. Therefore, this work provides a simple and scalable synthesis route for advanced oxygen storage materials.

A new monolithic Pt-Pd-Rh motorcycle exhaust catalyst to meet future emission standards

Abstract A new composite oxide material as support, CeO 2 -ZrO 2 -La 2 O 3 -PrO 2 -Al 2 O 3 , was synthesized by a co-precipitation method. Pd-Rh, Pt-Rh, and Pt-Pd-Rh supported on monolithic carrier catalysts were obtained by an impregnation route. The textural, structural, and reductive properties of the catalysts were characterized by N 2 adsorption-desorption, temperature-programmed reduction, oxygen storage capacity measurements, and X-ray diffraction. The air-fuel-ratio (A/F), space velocity (SV), and temperature characteristics of the fresh and aged catalysts were investigated on a systematic basis. The results showed that among the three catalysts, Pt-Pd-Rh displayed the best performance. For an SV of 40000 h −1 in the case of fresh Pt-Pd-Rh, the light-off temperatures ( T 50 ) for C 3 H 8 , CO, and NO were 239, 187, and 191 °C, respectively, with corresponding Δ T ( T 90 – T 50 ) values of 21, 3, and 3 °C, respectively. After aging, the T 50 for C 3 H 8 , CO, and NO were 298, 203, and 223 °C, respectively, and the Δ T values were 22, 5, and 13 °C, respectively. Moreover, the window widths for the A/F in the case of fresh and aged Pt-Pd-Rh catalysts were wide. Overall, the excellent performance for the Pt-Pd-Rh catalyst makes it suitable as a motorcycle exhaust catalyst, which can meet future emission standards.

Medium-Coupled Catalysts that Meet the Euro V Emission Standard for Gasoline Vehicles

Abstract The Ce 0.65 Zr 0.25 Y 0.07 La 0.03 O 1.95 oxygen storage material and La-stabilized alumina (La-Al 2 O 3 ) were prepared. After aging at 1000 °C for 5 h, Ce 0.65 Zr 0.25 Y 0.07 La 0.03 O 1.95 maintains excellent textural and oxygen storage properties, and after calcination at 900 °C for 4 h, La-Al 2 O 3 has superior textural properties. Medium-coupled Pt-Pd-Rh monolithic catalysts were prepared by impregnating Ce 0.65 Zr 0.25 Y 0.07 La 0.03 O 1.95 and La-Al 2 O 3 with Pt(NO 3 ) 2 , Pd(NO 3 ) 2 , and Rh(NO 3 ) 3 solutions and then washcoating on the cordierite honeycomb. The medium-coupled catalysts show high low-temperature activity and good thermal stability. The results from the emission test of a JETTA-MT vehicle show that the catalysts can meet Euro V emission requirements.

Medium-Coupled Catalysts Meeting Euro III Emission Standards for Condensed Natural Gas Vehicles

Abstract The Ce 0.45 Zr 0.45 Y 0.05 La 0.05 O 2 oxygen storage material and La-stabilized alumina (La-Al 2 O 3 ) were prepared. After aging at 1000°C for 5 h, Ce 0.45 Zr 0.45 Y 0.05 La 0.05 O 2 maintains superior textual and oxygen storage properties, and La-Al 2 O 3 has superior textual properties. Medium-coupled Pt-Rh monolithic catalysts for CNG vehicles were prepared by impregnating Ce 0.45 Zr 0.45 Y 0.05 La 0.05 O 2 and La-Al 2 O 3 with H 2 PtCl 6 and RhCl 3 solutions and then washcoated on the cordierite honeycomb. The medium-coupled catalysts showed high activity at low temperature and thermal stability. The results from the emission test of a JETTA-MT CNG vehicle indicated that the prepared catalysts were capable of fulfilling Euro III requirements.

Medium-Coupled Catalysts Meeting Euro III Emission Standards for Gasoline Vehicles

Abstract The Ce 0.5 Zr 0.4 Y 0.1 O 2 oxygen storage material and La-stabilized alumina (La-Al 2 O 3 ) were prepared. After aging at 1000

The influence of precipitation temperature on the properties of ceria–zirconia solid solution composites

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